The genus Bifidobacterium belongs to the Actinomycetaceae family; it groups together Gram-positive bacilli which are strict anaerobes fermenting glucose by the fructose-6-phosphate phosphoketolase pathway. Their optimum pH for growth is between 6 and 7, and their optimum temperature for growth is between 37 and 40° C.
Bifidobacteria are part of the normal human intestinal flora and they are recognized to have numerous beneficial effects on health. It is in particular known that breast-fed unweaned babies who possess an intestinal flora in which bifidobacteria are predominant are more resistant to infections and have in particular a lower risk of diarrhea than unweaned babies fed with industrial milk preparations.
The role of bifidobacteria in this increased resistance to infections has not been completely elucidated. Various studies indicate that they possess an immunostimulant power which would involve polysaccharide substances associated with the bacterial wall, or secreted by the bacteria during anaerobic fermentation. GOMEZ et al., [FEMS Microbiol. Lett., 56, 47-52, (1988)] describe the immunomodulatory effect of exocellular fractions rich in polysaccharides produced by Bifidobacterium adolescentis; FR Application published under the number 2652590, in the name of Laboratoires OM, describes an immunopotentiative exopolymer of a polysaccharide nature produced by Bifidobacterium infantis longum; HOSONO et al., [Biosci. Biotech. Biochem., 61, 312-316 (1997) and Bioscience Microflora, 17, 97-104, (1998)] describe immunopotentiator polysaccharides produced by various Bifidobacterium species. The immunomodulatory action of bifidobacteria also manifests itself by the regulation of the intestinal microflora, in particular at the expense of the development of pathogenic bacterial species. ROMOND et al., [Anaerobe, 3, 137-143, (1997), and J. Dairy Sci., 81, 1229-1235, (1998)] thus describe glycoprotein-rich fractions produced by Bifidobacterium breve under anaerobic fermentation conditions, and inducing in vivo a regulatory effect on the intestinal microflora.
Numerous products fermented by bifidobacteria, optionally combined with other lactic acid bacteria, exist on the market whose ingestion make it possible to benefit from the immunostimulant effects of bifidobacteria and of their fermentation products.
In the case of infant nutrition, however, they have the disadvantage of being too acidic and of having, in particular in the case of powdered products, a nonhomogeneous appearance after reconstitution, because of the coagulation of the milk proteins by the acidity generated during fermentation. They are therefore sometimes poorly accepted by the child or by the mother.
However, the inventors have now discovered that the production, by bifidobacteria, of substances having immunostimulant properties could be carried out without fermentation, and therefore without acidification of the final product.